Physical Quantities and Units | 9702 Physics Summary Notes

• 1. Physical Quantities and Units | 9702 Physics Summary Notes

 

1.1 Physical Quantities

· A physical quantity is made up of magnitude and unit

1.2 Base Units

· The following are base units:

Quantity			Basic Unit
Name	Symbol		Name	Symbol
Mass		m	Kilogram	kg
Length		l	Meter	m
Time		t	Second	s
Temperature		T	Kelvin	K
Electric Current		I	Ampere	A

· All units (not above) can be broken down to base units

· Homogeneity can be used to prove equations.

· An equation is homogenous if base units on left hand side are the same as base units on right hand side.

· This may not work every time due to the fact that it does not take pure numbers into account (Ek formula)

1.3 Multiples and Submultiples

Multiple	Prefix	Symbol
1012	Tera	T
109	Giga	G
106	Mega	M
103	Kilo	k
Submultiple	Prefix	Symbol
10-3	Milli	m
10-6	Micro	μ
10-9	Nano	n
10-12	Pico	p

 

 

1.4 Estimations

Mass of a person	70 kg
Height of a person	1.5 m
Walking speed	1 ms-1
Speed of a car on the motorway	30 ms-1
Volume of a can of a drink	300 cm3
Density of water	1000 kgm-3
Density of air	1 kgm-3
Weight of an apple	1 N
Current in a domestic appliance	13 A
e.m.f of a car battery	12 V
Hearing range	20 Hz to 20,000 Hz
Young’s Modulus of a material	Something  1011

1.5 Scalar and Vector

· Scalar: has magnitude only

e.g. speed, energy, power, work, mass, distance

· Vector: has magnitude and direction, can be –ve

e.g. displacement, acceleration, force, velocity, momentum, weight, electric field strength

1.6 Vectors